This invention relates to a fuel cell electrode.
According to one example of a fuel cell electrode, a layer of electroconductive particles having a catalyst is provided on a porous electroconductive substrate such as carbon paper or carbon filter cloth. Such an electrode is used in a fuel cell using phosphoric acid as an electrolyte or in a fuel cell using methanol or hydrazine as a fuel. The electrode is usually prepared by kneading electroconductive particles having a catalyst with a water-repellent polymer and a solvent, applying the resulting paste to the surface of an electroconductive substrate, and then drying and baking the substrate. U.S. Pat. No. 4,043,933 discloses one example of a process for preparing such an electrode.
As a result of investigation of such electrodes, the present inventors have found that a large number of fine cracks are formed on a catalyst layer at the drying or baking, and an electrolyte leaks into the electrode through the cracks.
In the catalyst layer of a fuel cell electrode, electrochemical reaction takes place at three-phase boundaries between the electrode catalyst, and electrolyte and diffused fuel gas, but when cracks are generated on the catalyst layer of the electrode, the electrolyte directly leaks into the cracks, so that the electrochemical reaction hardly takes place at the three-phase boundaries. Furthermore, generated cracks lower the strength of the catalyst layer, which is readily peelable from the substrate, considerably lowering the performance and life of fuel cells.